The present invention relates to a fireproof sheet glass, and more particularly to a fireproof sheet glass formed of glass composition which should be classified as a soda-lime glass.
Conventionally, no fireproof sheet glass of the above-noted type is known which achieves a high fireproof performance in the event of a fire. According to some conventional practices, an ordinary soda-lime glass composition would be formed into a wire glass to be utilized as a fireproof sheet glass, or a heat-tempered glass would be made from a soda-lime glass composition to be utilized as a fireproof sheet glass. Incidentally, although it is conceivable to form a fireproof sheet glass from one having a high melting point, such as borosilicate glass, such glass results in low productivity of the sheet glass due to its high melting point, high viscosity and so on. Further, if the glass contains boron, this will tend to reduce the life of the glass melting furnace. Therefore, there has been a demand for providing a fireproof sheet glass using soda-lime glass and there have been conducted intensive researches in this respect.
Incidentally, although the conventional fireproof sheet glass noted above achieves good fireproof performance at an earlier stage of fire, none are known to exist which can satisfy the requirement of A class fire door (according to a fireproof test based on Notice by Japanese Ministry of Construction Serial No. 1125). For instance, the fireproof sheet glass described above does not break when exposed to a fire, thus preventing spread of the fire. However, after lapse of a predetermined period of time, there is observed a phenomenon that the glass itself softens and will escape from e.g. a sheet-glass holding member (sash, frame). Thus, it cannot maintain its shape for 60 minutes according one requirement of the above standard.
Accordingly, an object of the present invention is to provide a fireproof sheet glass which uses soda-lime glass, yet which can satisfy the standard of A glass fire door.
The present inventors discovered that when a sheet glass is heated in accordance with the A class fire door standard, it can reach 770.degree. C.-780.degree. C. by the 60 minutes of heating and further that a sheet glass formed of a glass composition having a melting point of 780.degree. C. or higher has greater possibility of conforming to the above standard.
Then, the present inventors employed, as a fireproof sheet glass, a following glass composition (wt.%) having superior fire resistance previously developed by the present inventors and newly found out that this can suitably satisfy the above standard. Namely;
______________________________________ SiO.sub.2 56.about.68% Al.sub.2 O.sub.3 0.2.about.5% ZrO.sub.2 0.about.3% Li.sub.2 O 0.about.0.5% Na.sub.2 O 0.2.about.4% K.sub.2 O 6.about.14% MgO 1.about.14% CaO 6.about.12% SrO 0.about.12% BaO 0.about.13% ZnO 0.about.2%; and; Na.sub.2 O + K.sub.2 O 8.about.14% MgO + CaO 8.about.15% SrO + BaO 8.about.14% MgO + CaO + SrO + BaO 20.about.27% SO.sub.3 + Sb.sub.2 O.sub.3 0.about.1% and; ______________________________________
the composition has an average thermal expansion ratio at 50.about.350.degree. C. of 75.about.95.times.10.sup.-7 /K;
the composition has a warping point of 540.degree. C. or higher; and
the composition has a 10.sup.2 poise temperature of 1560.degree. C. or lower.
Then, for accomplishing the above-noted object, a fireproof sheet glass, according to the characterizing features of the present invention, comprises a composition, in the unit of wt. % of
______________________________________ SiO.sub.2 56.about.68% Al.sub.2 O.sub.3 0.2.about.5% ZrO.sub.2 0.about.3% Li.sub.2 O 0.about.0.5% Na.sub.2 O 0.2.about.4% K.sub.2 O 6.about.14% MgO 1.about.14% CaO 6.about.12% SrO 0.about.12% BaO 0.about.13% ZnO 0.about.2%; where, Na.sub.2 O + K.sub.2 O 8.about.14% MgO + CaO 8.about.15% SrO + BaO 8.about.14% MgO + CaO + SrO + BaO 20.about.27% SO.sub.3 + Sb.sub.2 O.sub.3 0.about.1% and; ______________________________________
the composition has an average thermal expansion ratio at 50.about.350.degree. C. of 75.about.95.times.10.sup.-7 /K;
the composition has a warping point of 540.degree. C. or higher;
the composition has a 10.sup.2 poise temperature of 1560.degree. C. or lower; and
the composition has a softening point of 780.degree. C. or higher.
Incidentally, in the composition as above, preferred ranges are conceivable for the respective components thereof. Specifically, it is preferred that the melting point of the glass (10.sup.2 poise temperature) be below 1560.degree. C. More preferably, the respective components of the composition should be adjusted to render the melting point 1550.degree. C. or lower. Similarly, regarding the viscosity of the glass composition, it is preferred that an appropriate viscosity be obtained at an inlet opening to a float bath in case the sheet glass is formed by the float process for example. As a condition for this, it is preferred that the respective components be adjusted so as to obtain 10.sup.4 poise temperature (working temperature) of 1140.degree. C. or lower. It is also preferred that the average thermal expansion at 50.about.350.degree. C. range at 75.about.95.times.10.sup.-7 /K, more preferably at 80.about.90.times.10.sup.-7 /K. Further, as it is desired to set the devitrifying temperature so as not to cause devitrification during forming of the glass, it is preferred that the respective components be adjusted so as to obtain a devitrifying temperature of 1140.degree. C. or lower. For these purposes, the contents of the respective components should preferably adjusted as follows.
If the content of SiO.sub.2, which is the network former of the glass, is below 56 wt. %, this will result in lowering of the warping point of the glass. Hence, it is preferred that this be present at 58 wt. % or more. Conversely, if the content of SiO.sub.2 exceeds 58 wt. %, this will result in reduction in the thermal expansion ratio of the glass and also to difficulty in its tempering when this glass is heat-tempered for use in fire prevention.
Al.sub.2 O.sub.3 is a component effective for elevating the warping point of the glass. This is also effective, even in a small amount of addition, for improving devitrification and water-resistance properties of the glass. Al.sub.2 O.sub.3 can provide only a limited effect if present below 0.2 wt. %. Hence, at least 0.2 wt. % or more thereof is needed. And, using it at 0.5 wt. % or more is preferred for significantly improving the devitrification and water-resistant properties. In general, in a portion of inner lining of a melting furnace, alumina type bricks are employed. After having melted glass for a long period of time, the bricks will erode, leading to increase in the concentration of alumina adjacent the bricks. Especially, the glass composition to which the present invention pertains contains large amounts of alkaline metal oxides and alkaline earth metal oxides, so that the erosion of bricks tend to be promoted. In case glass contains a large amount of Al.sub.2 O.sub.3, the concentration of Al.sub.2 O.sub.3 increases with development of brick erosion. As a result, there occurs devitrification due to the Al.sub.2 O.sub.3 component, thus deteriorating the quality of the glass. For this reason, Al.sub.2 O.sub.3 should be present at 5 wt. % or less, more preferably at 4 wt. % or less.
Al.sub.2 O.sub.3 , Zro.sub.2 also is a component effective for elevating the warping point of the glass. However, as ZrO.sub.2 affects the physical properties of the glass as is the case with Al.sub.2 O.sub.3, it is not an essential component in the present invention. Notwithstanding the above, since it is effective, in a small addition amount, for improving the water-resistance of the glass, it is preferred that ZrO.sub.2 be used at 0.2 wt. % or more, more preferably at 0.3 wt. % or more.
Generally, alumina type bricks and zirconia type bricks are employed in the inner lining of the melting furnace. Thus, if the furnace has melted glass containing a large amount of ZrO.sub.2 for an extended period of time, just like Al.sub.2 O.sub.3, there will occur devitrification due to ZrO.sub.2, leading to deterioration of the quality of the glass. For this reason, it is preferred that ZrO.sub.2 be present at 3 wt. % or less, more preferably at 2.5 wt. % or less.
MgO is effective not only for improving the solubility, but also for elevating the warping point. MgO provides only an insufficient effect below 1 wt. % and it is preferred that MgO be present at 2 wt. % or more. However, if the amount of MgO exceeds 7 wt. %, devitrification will likely occur. So that, preferably, the content of MgO should be 6 wt. % or less.
Like MgO, CaO is effective not only for improving the solubility, but also for elevating the warping point. CaO provides only an insufficient effect below 6 wt. % and it is preferred that CaO be present at 7 wt. % or more. However, if the amount of CaO exceeds 12 wt. %, devitrification will likely occur. So that, preferably, the content of CaO should be 10 wt. % or less.
The combined amount of MgO and CaO is 8 wt. % or more in order to improve the solubility and to elevate the warping point. Thus, it is preferred that the combined content of MgO and CaO is 9 wt. % or more. However, if the content exceeds 15 wt. %, devitrification will likely occur. So that, preferably, the content should be 13 wt. % or less.
SrO is not essential but may be effective for improving the solubility and also for raising the warping point. Thus, it is preferred that SrO be present at 2 wt. % or more. However, if the content exceeds 12 wt. %, this will result in increase in the specific weight and also raw material cost. Therefore, it is more preferred that SrO be present at 10 wt. % or less.
BaO, though not essential, is effective for improving the solubility. Thus, it is preferred that BaO be present at 2 wt. % or more However, if this is present at 13 wt. % or more, this will result in increase in the specific weight and also raw material cost. Therefore, it is more preferred that it be present at 10 wt. % or less.
BaO+SrO is needed for further improving the solubility which otherwise would be insufficient only by MgO+CaO and needed also for increasing the expansion coefficient together with Na.sub.2 O+K.sub.2 O. If below 8 wt. %, the effect will be insufficient. Hence, the content should preferably be 10 wt. % or more. Conversely, if the content exceeds 14 wt. %, this will tend to invite devitrification as well as increase in the raw material cost.
A combination of MgO, CaO, Sro, and BaO.
This is effective for improving the solubility of the glass. If the total content is below 20 wt. %, the desired melting temperature cannot be obtained. Hence, it should preferably be 21 wt. % or more. Conversely, if the content exceeds 27 wt. %, this will elevate the devitrifying temperature of glass excessively, presenting difficulty in the plate forming operation. Thus, the content should preferably be 26 wt. % or less.
ZnO is effective for improving solubility, but it tends to easily evaporate to reduce the life of melting furnace. Therefore, the content should preferably be 2 wt. % or less, more preferably 1 wt. % or less.
This component lowers the melting point, but it lowers the warping point to a greater degree. Hence, the content should preferably below 0.5 wt. %, or more preferably substantially zero or below 0.2 wt. %.
This component is effective for improving the solubility and also for increasing the thermal expansion ratio. Further, Na.sub.2 O in cooperation with K.sub.2 O, is effective also for improving the water resistance. Its effect will be insufficient below 0.2 wt. %. Hence, it should preferably be present at 0.5 wt. % or more. However, even with a small addition amount, the component can significantly lower the warping point and also promote the erosion of bricks. Therefore, the content should be limited at 4 wt. % or less, preferably 3.5 wt. % or less, more preferably 3 wt. % or less or even more preferably 2 wt. % or less.
K.sub.2 O is a component effective for increasing the thermal expansion ratio and also for elevating the warping point. The effects will be insufficient below 6 wt. %. Hence, the content should preferably be 7 wt. % or more, more preferably 9.5 wt. % or more. However, if the content exceeds 14 wt. %, this will tend to invite devitrification as well as deterioration in the water-resistance. Therefore, it is preferred that the content be 11 wt. % or less.
A combination of N.sub.2 O and K.sub.2 O is essential for improving the solubility, particularly for increasing the thermal expansion ratio. If the total content is below 8 wt. %, this will result in excessively small thermal expansion ratio. Hence, the content should preferably be 9 wt. % or more, more preferably 10 wt. % or more. On the other hand, if the content exceeds 14 wt. %, this will lower the warping point or elevate the devitrifying temperature. Hence, it is preferred that the content be 13 wt. % or less.
Though not an essential component, TiO.sub.2, if present, may be effective for improving the chemical durability. A content of 3 wt. % or more is undesirable, as it will result in coloring of the glass.
For the reasons set forth above, according to the more preferred characterizing features of the present invention, the composition of the fireproof sheet glass for achieving the object are, in the unit of wt. %:
______________________________________ SiO.sub.2 from 56% to about 68% Al.sub.2 O.sub.3 from 0.2% to about 4% ZrO.sub.2 from 0% to about 2.5% Li.sub.2 O from 0% to about 0.5% Na.sub.2 O from 0.2% to about 3.5% K.sub.2 O from 7% to about 11% MgO from 2% to about 6% CaO from 6% to about 10% SrO from 2% to about 10% BaO from 2% to about 10% ZnO from 0% to about 2% and; Na.sub.2 O + K.sub.2 O from 8% to about 14% MgO + CaO from 8% to about 15% SrO + BaO from 8% to about 14% MgO + CaO + SrO + BaO from 20% to about 27% SO.sub.3 + Sb.sub.2 O.sub.3 from 0% to about 1% ______________________________________
the composition has an average thermal expansion ratio at 50.about.350.degree. C. of 75.about.95.times.10.sup.-7 /K;
the composition has a warping point of 550.degree. C. or higher;
the composition has a 10.sup.2 poise temperature of 1550.degree. C. or lower; and
the composition has a softening point of 780.degree. C. or higher.
Even more preferably, in the unit of wt. %;
______________________________________ SiO.sub.2 58.about.66% Al.sub.2 O.sub.3 0.5.about.4% ZrO.sub.2 0.2.about.2.5% Li.sub.2 O 0.about.0.1% Na.sub.2 O 0.5.about.3% K.sub.2 O 8.about.11% MgO 2.about.6% CaO 6.about.10% SrO 2.about.10% BaO 2.about.10% ZnO 0.about.1%; and; Na.sub.2 O + K.sub.2 O 9.about.13% MgO + CaO 9.about.13% SrO + BaO 10.about.14% MgO + CaO + SrO + BaO 21.about.26% SO.sub.3 + Sb.sub.2 O.sub.3 0.about.1% and; ______________________________________
the composition has an average thermal expansion ratio at 50.about.350.degree. C. of 80.about.90.times.10.sup.-7 /K;
the composition has a warping point of 550.degree. C. or higher;
the composition has a 10.sup.2 poise temperature of 1550.degree. C. or lower; and
the composition has a softening point of 780.degree. C. or higher.
With the above-described compositions, the fireproof sheet glass described above provides high heat resistance and also a high softening point of 780.degree. C. or higher. Hence, this glass, when subjected to the fireproof test according to the A class fire door, the glass can effectively endure without being broken. Further, after lapse of the predetermined time period, there hardly occurs such phenomenon of the glass per se being softened and escaping from the sheet-glass holding member (sash, frame) or the like.
Further, according to a further feature of the invention, when the glass is formed as a sheet glass, this may be a wire sheet glass or subjected to a heat-tempering treatment.
If the fireproof glass is provided as a wire glass, the fireproof performance may be further improved and the fireproof performance may be improved by the heat-tempering treatment as well.
Moreover, in the case of a melting operation at a melting temperature of 1560.degree. C. or lower and a working temperature of 1140.degree. C. or lower using bricks containing alumina, the glass will less likely devitrify in the vicinity of these bricks. Further, since the glass is formed of the glass composition having the property of its working temperature being higher than the devitrifying temperature, continuous production of quality glass by the float process is possible, so that the advantage of high productivity may be attained.